I have had only three dreams that I knew beyond a doubt (In my mind, at least) what the meanings were. My "knowing" beyond a shadow of a doubt came from the Holy Spirit, I think.....because I was praying for the holy spirit to show me such and such, and I felt very at peace with the direction I got from my dream. It was "spot on" understanding.

Like Wendy, when I have a dream where I know the meaning it's usually because I'm at peace with the interpretation. Other times, I may not know the meaning immediately, but I will have an experience at a later time that makes me think of the earlier dream and there's that quickening in the spirit...you just know that the two are related...sorry that description isn't more tangible..but it's a feeling in your spirit...the final way you know the interpretation is if the dream manifests, i.e., it was a prophetic dream and the dream (or portions of it) came to pass...

I usually know what my dream means, when i feel at peace with an interpretation as well. Sometimes i recieve interpretations while im half asleep. Its easier to hear the Lord when my thoughts or opinions are cleared from my mind.